Although the underlying causes of glaucoma are not fully understood at this time, glaucoma is characterized by damage to the optic nerve head, accompanied by a decrease in the normal visual field. One risk factor for glaucomatous visual field loss is elevated IOP. In fact, glaucoma has historically been treated by drug and/or surgical therapy to lower elevated IOP. While elevated IOP has been positively correlated with the rate of progression of visual field loss in glaucoma, visual field loss may occur at levels of IOP which are considered within the normal range. Thus, other factors, alone or in addition to elevated IOP, may influence the occurrence and rate of progression of visual field loss.
To remain healthy and function normally, the retina and the optic nerve head fibers (neurons) must receive a proper supply of nutrients and oxygen, and must have their carbon dioxide and other metabolic waste products removed. This is accomplished by the microcirculation in these tissues. As used herein, the term "microcirculation" refers to the blood flow through the nutritive blood vessels, across whose walls nutrients, gases and waste products move. Blood flow to the eye depends upon the pension pressure (the systemic blood pressure may the IOP). Some tissues have the ability to maintain (i.e., autoregulate) blood flow through a range of perfusion pressures such that an increase in systemic blood pressure may cause a reduction in the caliber of the blood vessel lumen. Conversely, reduction in systemic pressure in such tissues can result in vessel dilation; however, there is a point where perfusion pressure falls to such a level that the vessel is maximally dilated. Any further fall in perfusion pressure results in a reduction of blood flow to the tissue (ischemia). Ischemia may also result from obstruction, vasospasm, increased vascular resistance, or other interference with microcirculation. Prolonged ischemia ultimately can result in tissue necrosis or neuronal cellular apoptosis. In the case of the optic nerve head or retina, a state of visual dysfunction may precede the death of the neurons. Hence, if ischemia is involved in the death of optic nerve fibers due to glaucoma or some other ischemic-borne retinopathies or optic neuropathies, then its prevention could protect the neurons from death or loss of function.
The vasodilatory and spasmolytic activities of certain isoquinolinesulfonyl compounds have been described with respect to non-ocular tissues. See, e.g., EP 0 187 371 B1, which corresponds to U.S. Pat. No. 4,678,783. These vascular attributes are likely associated with inhibitition of myosin-light chain kinase activity. Myosin-light chain kinase is an enzyme necessary for the excitation-contraction coupling of contractile activity in vascular smooth muscle. Inhibition of this enzyme results in vascular smooth muscle relaxation (i.e., vasodilation) which can produce an increased blood flow.